Stormwater home page City of Los Angeles home page
      Department of Public Works Bureau of Sanitation

Los Angeles’ storm drain system is a vast network of underground pipes and open channels that were designed to prevent flooding. Runoff drains from the street, into the gutter, and enters the system through an opening in the curb called a catch basin. Catch basins serve as the neighborhood entry point to the journey into the ocean.

The storm drain system receives no treatment or filtering process and is completely separate from Los Angeles’ sewer system.

The graphics at left show the path sequence that urban runoff takes as it travels through the storm drain system.

Los Angeles’ storm drain system is a 1,500-mile network of underground pipes and channels that discharge directly into our coastal waters.

Curbside catch basins are the primary points-of-entry for urban runoff. From there, runoff…
…flows into underground tunnels that empty into…
…flood control channels such as Ballona Creek or the Los Angeles River. The flood control channels eventually discharge to…
…over 65 shoreline outfalls rimming our coast.


The original storm drain system was developed in the 1930 by the Army Corps of Engineers. As the City began to grow rapidly in the 1920s and 1930s, rainwater that was once absorbed by miles of undeveloped land began to run off the newly paved and developed areas, leading to an increased amount of water flowing into Los AngelesÕ rivers and local creeks. These waterways could not contain the increased amount of water and the region experienced extensive flooding. In response, the Army Corp of Engineers lined the Los Angeles River and Ballona Creek with concrete and initiated the development of an underground urban drainage system. As Los Angeles continued to grow, a complex drainage system developed.

Today, a total of 35,000 catch basins, over 1,500 miles of underground pipes, and 100 miles of open channels comprise the City’s storm drain system. In total, runoff from approximately 1,060 square miles of developed land reach Santa Monica and San Pedro Bays through approximately 60 storm drain outfalls. Approximately 100 million gallons of water flow through Los Angeles’ storm drain system on an average dry day. When it rains, the amount of water flowing through the channels can increase to 10 billion gallons reaching speeds of 35 mph and depths of 25 feet.


City crews have found an unusual collection of items that have been dumped or have made their way into storm drain channels. These items include:

Ping Pong Table Purses
Motorcycle Wallets
Automotive Parts Mattresses
Stuffed Animals Bicycles and Tricycles
Shopping Carts Basketballs, Baseballs, and Golf Balls
Baby Strollers


In the Tarzan movies from the early 1930’s, the unlined areas of the storm drain channels were actually used for many of the canoe scenes. More recent Hollywood productions that feature scenes filmed in the storm drain flood channels include Grease, Terminator II, Point Break, Volcano, and the sci-fi classic Them.

For more information about the storm drain system, visit the following pages within the City of Los Angeles’ Stormwater Program web site: